Refractory silica bricks or molded silica products traditionally have been prepared by energy-intensive methods that require costly kilns, high consumption of fuel and carefully regulated chemical formulation, preheating, firing and cooling cycles to achieve reproducible quality products. Various calcium aluminate and calcined alumina cement and refractory molding products have been produced, but none of these has achieved the combined properties of fast curing, high adhesive bonding qualities, low material cost, universal raw material accessibility or availability, together with good mechanical, thermal and chemical properties. Thus, a need exists for a product that combines the above qualities with simplicity of use so as to preclude any special skill or training to accommodate the product to various uses.
Among the uses inherent to a product of the nature herein described are rapid repair of roadways and runways without special pretreatment or conditioning to assure adhesion to old concrete and earthen surfaces; a brick mortar which provides a bond strength often greater than the tensile strength of brick, making it possible to prefabricate tilt-up walls which can be mass produced offsite and delivered intact to job sites; repair or construction of moderately high temperature kilns; production of refractory bricks; production of mortar for bonding refractory bricks; production of cast-in-place structures capable of high temperature exposure having appropriate accommodation for thermal expansion; and chemically resistant coatings for pipes, reactor vessels, storege tanks and the like which exhibit excellent adhesion to metal, resistance to abrasion and inertness to most concentrated mineral acids. The cement or molding product of the nature disclosed herein is chemically compatible with glass fibers thereby allowing such fibers to be used as reinforcement, the resulting product having outstanding structural and mechanical properties.
In the field of art to which the present invention pertains, applicant is aware of U.S. Pat. Nos. 3,138,471, 3,450,548, 3,490,931, 3,813,253, 3,829,320 and an article entitled "Acid Resistant Concrete" by M. S. Crowley and J. F. Wygant, Chemical Engineering Progress, pages 44-48, Feb., 1968. Of the foregoing, Applicant deems the most pertinent to be U.S. Pat. Nos. 3,138,471 (the '471 patent), 3,450,548 (the '548 patent) and 3,490,931 (the '931 patent).
The '471, '548 and '931 patents are each directed to chemically setting, acid-resistant cemant products containing silicate of soda as a binder. These patents all disclose a silica-to-soda ratio of 3.01:1 to 3.22:1. It has been found in practice that these ratios provide products inferior to the present invention from the standpoint of poor adhesion to other cements and metals. The cements disclosed in these three patents are very fast setting and consequently are not particularly adaptable for the domain of applications needed for an adhesive and high temperature cement. The typical setting time of 15 minutes for these prior art products does not provide adequate working time for the cements. Even the '931 patent product containing a retardant allows only 45 to 75 minutes working time.
The cement slurries resulting from the process disclosed by the '471, '548 and '931 patents are extremely thick and cannot be easily trowled, sprayed or molded. They have the viscosity of bread dough, and any extra water added to decrease viscosity reduces the strength as outlined on page 44 of the referenced Crowley article. The compositions all prescribe about 13% total water including the water in the sodium silicate solution, and the compressive strength of the product of these compositions is 2,500 pounds per square inch (psi) with this percentage of dilution. The disclosed recipes of these three patents which provide compressive strengths of over 2,500 psi cannot be molded without the use of a compaction device such as would compress a damp cake into a cube or testing. Thus it is apparent that the formulations of the '471, '548 and '931 patents have definite limitations.